Vibrator system



Aug. 29, 1961 B. PETZELT 2,998,562

VIBRATOR' SYSTEM Filed March 12, 1959 INVENTOR. BedrQb/z PeZze/i2,998,562 VIBRATOR SYSTEM Eedrich Petzelt, Prague, Czechoslovakia,assignor to Lahcratorni pristroje, narodni podnik, Prague,Czechoslovalda Filed Mar. 12, 1959, Ser. No. 798,955 Claims priority,application Czechoslovakia Mar. 14, 1958 1 Cliam. (Cl. 321-49) Thepresent invention relates to a vibrator system supplying an interrupteddirect current to a transformer for producing alternating current.

It is an object of this invention to provide a vibrator system of thekind which operates at maximum efficiency when the source of directcurrent or the circuit including this source is of high resistance.

When measuring or registering certain electric valum with direct currentapparatus A.C. amplifiers are frequently used, which are supplied over avibrator and which are provided with an input transformer as couplingelement between the vibrator and the first electron valve of theamplifier. The use of resistance or capacitor coupling brings a numberof drawbacks. In most cases, there is required a large input impedancewhich may be only to a certain degree achieved by the increase of theimpedance of the input transformer, for instance by increasing thenumber of turns of the coils, by the use of larger iron cores of specialmaterial and similar.

A substantial increase of the input impedance cannot be however achievedby this method, as a correctly functioning vibrator is short circuitedwithin a certain interval which amounts approximately to of one cycle.In the course of this time the source of the direct current is shortcircuited over the relatively low ohmic resistance of the primarywinding of the input transformer.

In accordance with this invention a substantial increase of the inputimpedance is achieved by introducing an ohmic resistance into thecircuit of the primary Winding of the input transformer. This resistancemay be placed at difierent places of this circuit and may be evenrepresented by an increased ohmic resistance of the primary winding ofthe input transformer.

The accompanying drawing shows by way of example a wiring diagram of anarrangement according to this invention.

The measured D.C. value is supplied to the terminals A, B and charges acondenser C over a resistance R,,. From the terminals of this condenserC the primary winding L of the input transformer is supplied over thecontacts D, E, F of a vibrator and over a resistance R which isconnected to the central tap of the primary winding L of thetransformer. The secondary winding L of this transformer supplies thegrid circuit of an electron valve G.

Let it be assumed that the input impedance of the transformer, i.e. ofhalf of the primary winding, is R, that the corresponding ohmicresistance of this part of the winding is R the period within which allcontacts D, E, F of the vibrator are short circuited is z, expressed asa fraction of the entire cycle, R the additional resistance, R theresulting resistance of the circuit during the short circuit period (z),and R the resulting resulting resistance of the circuit during theremaining part of the cycle (1z).

The said resistance R is equal to as current passes through bothbranches of the primary winding L The resistance R is equal to R -l-R Onthe terminals of the capacitor C of sufiicient magnitude a voltage 2 ispresent, which corresponds to the mean nited States Patent C 52,998,562Patented Aug. 29., 1961 ICC value of the resistance of the circuitwithin the whole cycle.

The mean value of the resistance if the voltage of the source of directcurrent e =1, then the voltage e on the terminals of the capacitor Cwill be a T+ R.) Ri+ Rx) e achieves its maximum value for for whichcondition we obtain the equation If for instance Z= 0 R =200K ohm R =2Kohm R =1200K ohm R, =43.5K ohm e 2 0.41

for R =0, i.e. if there is no additional resistance introduced into thecircuit of the primary winding of the transformer We have therefore afive time increase of the voltage on the primary winding as compared tothe same circuit without resistance.

The said vibrator system is particularly useful when measuring voltagesof sources of direct current with high internal resistance, or over ahigh resistance, for instance over a filter with RC elements, where theintroduction of the additional resistance R into the circuit of theprimary winding of the transformer represents a substantial increase ofthe voltage across the input terminals of the transformer and thereforea substantial increase of the sensibility of the apparatus.

The said resistance R may be placed at any suitable place in the circuitof the primary winding of the transformer, for instance into bothbranches leading from the outer terminals of the primary winding L tothe contacts E, F or into the branch leading to the vibrator contact D,as shown on the drawing in broken lines. Finally the resistance R may berepresented by the winding L of the transformer, which may be wound of aresistance wire.

What I claim is:

In combination in a system for converting a direct-current voltage to bemeasured into an alternating-current voltage, a vibrator including twospaced contacts and vibratable contact means movable relative to saidcontacts between successive positions of engagement with only one ofsaid contacts, of simultaneous engagement with both of said contacts,and of engagement with only the other one of said contacts, atransformer including a primary and a secondary winding, said primarywinding having two outer terminals and a center tap terminalintermediate said outer terminals, two conductors respectivelyconnectmeans for respectively connecting said center tap terminal andsaid contact means to the two poles of a source of direct-currentvoltage to be measured, said contacts, contact means, primary winding,conductors, and conductor means constituting an input circuit, saidinput circuit including fixed resistance means for maintaining theimpedance of said circuit above a predetermined minimum value when saidvibratable contact means is engaged with both of said contacts, saidresistance means having the of the source whose voltage is to bemeasured, and R is the input impedance of one-half of said primarywinding, and a capacitor one of Whose terminals is connected to saidcontact means and the other of whose terminals is connected to a pointbetween said fixed resistance means and R.,, whereby the average voltageappearing acrosssaid secondary winding during a complete cycle ofoperation of said vibrator is optimized.

References (Iited in the file of this patent UNITED STATES PATENTS2,237,003 Kiltie Apr. 1, 1941 2,284,794 Bedford June 2, 1942 2,423,524Side July 8, 1947 2,485,948 Williams et al. Oct. 25, 1949 2,773,946Greenberg Dec. 11, 1956 2,891,220 Wannamaker June 16, 1959

